Overhead projectors

ABSTRACT

The objective of the invention is an overhead projector (1) supplied with acetate film rolls (4), to which projector belongs a body (2) onto which is fixed a projection arm (16) equipped with a lens/lenses (21) and a flat mirror (20). The body (2) is supplied with an openable top part (3) into which roll spaces are arranged for the acetate film rolls (4). The acetate film rolls (4) are installed on axle rods (26) which are supplied with rotating cylinders (5) and mounted in the top part (3) at opposite ends in the shaped spaces with the aid of a bent spring and fixing hole. In the inner side of the body (2) is also arranged at least one shutter screen element (10-13) that stays inside the body (2) in all cases of use, and which is installed to cover the projected part of the acetate film (6) fully or partially. The screen elements are moved in a flat level on guiding rods (15 ) inside the body (2) in the directions of the length and/or width of the body (2) with the help of levers (14).

The objective of this invention is an overhead projector (OHP) fittedwith an acetate film roll, which consists of a body and its relevantprojection arm fitted with a lens or lenses and a mirror.

In the existing OHP's, the acetate film rolls are usually assembled asextra elements onto fixed holders. These holders are usually fixed ontothe body of the projector. One disadvantages of fixing the acetate filmrolls in this conventional way is that when it is necessary to performmaintenance work, like changing a lamp, it is necessary to take therolls off before being about to open the top and have access to theinside of the body. There is a further problem in the conventional OHP'sand that is that when there is a need to cover part of the projectedimage, like in lectures and demonstrations, this is done by using extrasheets of paper or equivalent on top of the image. This makes the use ofthe OHP quite clumsy.

The main objective of the invention being presented is to decrease oreliminate the above causes of problems or disadvantages, and generallyto improve the usefulness of the OHP. In order to implement the mainobjectives of the invention, the items presented in the patent claim 1are characterized of the OHP.

The invention is shown in relation to the enclosed drawings as follows:

FIG. 1 shows the OHP, according to the invention, open and presented ina perspective view.

FIG. 2 shows the OHP, according to the invention, closed and presentedin a perspective view.

FIG. 3 shows some features of the OHJP, according to the invention,viewed from FIG. 2, arrow A.

FIGS. 4 and 5 shows, according to the invention, the OHP's projectionarm, with its fixing base and moving knob seen from front and top.

FIG. 6 shows some details of the invention seen from the top.

According to FIG. 1 and 2, the OHP consists of a body 2, which issupplied with an openable top part 3. Onto the body 2 is also connecteda projection arm 16 with the help of a fixing base 18 and the movingknob 17. The top part of the projection arm 16 is made of a base unit22, lens/lenses 21 and a flat mirror 20 on a holder 19. The openable toppart 3 is supplied with a glass plate 8 with its holder and the acetatefilm rolls 4 with their holders. According to FIG. 3, the acetate filmrolls are installed on axle rods 26, which are supplied from one endwith rotating cylinders 5. The acetate film rolls 4, which are installedon the axle rods 26, are mounted in the openable top part 3 at oppositeends in the shaped spaces with the help of a bent spring 27 and fixinghole 28. The roll space is spaced so that when the top part 3 is in theclosed position, the acetate film rolls 4 can be rotated from therotating cylinder 5. The openable top part 3 is fixed to the body 2 witha hinge 9.

In the inner part of the body 2 is arranged four shutter screens 10-13advantageously. The screens can be moved in a flat level with guidingrods situated in the inner side of the body 2 on all four sides so thatthe screens 10-13 stay, in all cases of use, inside the body 2.According to FIGS. 1 and 6, the form of operation of screens 10 and 12is such, that they move in the same direction as the movement of theacetate film, while screens 11 and 13 move in a direction perpendicularto that of the movement of the acetate film. Each of the shutter screens10-13 is so arranged that it can, when needed, cover all the area of theimage being projected. The shutter screens 10-13 are moved with the helpof the levers 14, which are easily situated in two adjacent sides of thebody 2 of the OHP 1. In the inside of the body 2 is also installed aFresnel lens 7 between the edge rims 26 and 24. The openable top part 3is locked with the aid of the locking unit 23.

The projection arm 16 is a square section aluminum tube whose top partis bent so that the base unit 22 is always maintained in a level exactlyparallel to the glass plate 8. The projection arm 16 is fixed to thebody 2 with the fixing base 18. The fixing base 18 is a cylindricallyshaped plastic piece into which is cut a vertical hole 18b of the samesquare section of the projection arm 16, and in the other direction iscut a cylindrical hole 18a perpendicular to the square section hole. Thefixing base 18 is itself fixed to the body 2 by screws or rivets. Themoving knob 17 consists of a cylindrical part 17b and a rim 17a, to beinserted into hole 18a. Between these rims 17a, the projection arm 16 issituated.

By turning the moving knob 17, the projection arm 16 moves vertically.

According to the invention, the OHP is also supplied with an electroniccircuit which measures the light condition in the room and adjusts theintensity of the lamp of the OHP 1 accordingly. The light intensityneeded in a dark room from the lamp of the OHP 1 is less than that in alit room, and in this case the light intensity of the lamp can bedecreased, thus extending the life of the lamp noticeably.

In order to improve the moving, storage and handling of the OHP, aretracting power cable is installed in the OHP.

I claim:
 1. An overhead projector (1) comprising:a box-like body (2)having an openable top part (3) with a window through which lightprojection may occur; a projection (16) arm mounted on said body andequipped with at least one lens (21) and a mirror (20) for receiving thelight projecting through said window; transparent film rolls (4) atopposing ends of said top part and having a transparent film extendingbetween said rolls and across said window so that information on saidfilm appearing in said window may undergo projection; said top partbeing formed to receive and retain said rolls in appropriately shapedspaces at the opposing ends of said top part, each of said rolls havingan axle (26) at one end and an axially extending cylindrical end portion(5) by which said roll can be manually rotated, each of said axles beinglocated in a hole (28) in said top part for rotatably mounting saidrolls in said spaces, said other ends of said rolls being biased by bentsprings (27); and shutter screen means mounted inside said box-like bodyand capable of blocking at least a portion of said window, said shutterscreen means comprising two pairs of opposing shutters (10,12; 11,13),the shutter of each pair being movable toward and away from each otheralong paths lying generally parallel to said window on guide rods (15)provided in said body; said shutter screen means having handles (14)coupled to said shutters and extending outside said body along two sidesthereof for moving said shutters.
 2. An overhead projector, according toclaim 7, wherein said projection arm (16) has a smooth exterior, andwherein said projection arm is mounted on said body by means of a fixingelement (18, 18a, 18b) affixed to said body and embracing saidprojection arm, and a moving element (17, 17a, 17b) rotatably mounted insaid fixing element and frictionally engaging said projection arm.
 3. Anoverhead projector, according to claim 2, characterized in that theprojection arm (16) is square in cross section.
 4. An overheadprojector, according to claim 2, characterized in that the material ofthe projection arm (16) is aluminum or aluminum alloy.
 5. An overheadprojector according to claim 1, including a lamp in said box-like bodyand means for sensing the ambient light conditions in which saidoverhead projector is used and adjusting the intensity of said lampaccordingly.
 6. An overhead projector according to claim 1,characterized in that the overhead projector (1) is provided with aretracting power cable.
 7. An over projector according to claim 3,characterized in that the material of the projection arm (16) isaluminum or aluminum alloy.